The formula
For every activity: emissions (kg CO₂e) = activity quantity × emission factor. The emission factor is published by your national environment agency and tells you how many kilograms of CO₂-equivalent each unit of activity releases.
Step 1 — Gather your activity data (one year)
- Home energy: annual kWh of electricity and gas (last 12 utility bills).
- Car: kilometres driven and fuel type.
- Flights: number of short/medium/long-haul flights, return.
- Diet: rough weekly servings of beef, dairy, chicken, fish, plant.
- Goods & services: total spend by category, or skip and use a country average.
Step 2 — Apply official emission factors
The most-trusted sources by country:
- UK — DEFRA conversion factors
- US — EPA Emission Factors Hub
- Germany — Umweltbundesamt (UBA)
- France — ADEME Base Empreinte
- Spain — MITECO
- Mexico — INECC
Step 3 — Sum and benchmark
Add up every activity's emissions, then compare the total to your country's per-capita average (8.5 t in the UK, 13 t in the US, 7 t in France). That comparison tells you whether you're above or below average and where the biggest gaps are.
Or just use a calculator
Doing this by hand for a year takes 1–2 hours. Our free carbon footprint calculator applies the same official factors automatically in 30 seconds, and the carbon tracker updates the number as you log meals and trips.